1. Technical Field
The present application relates to a method to assemble a transmitter optical sub-assembly (hereafter denoted as TOSA), in particular, the application relates to a TOSA having a function of the wavelength division multiplexing (hereafter denoted as WDM).
2. Prior Arts
Various TOSAs implemented with the WON function have been disclosed. For instance, U.S. Pat. No. 8,036,533B, has disclosed a TOSA with optical sources, arrayed lenses, and an optical multiplexer where they are enclosed within a package. Optical beams coming from respective optical sources are collimated by arrayed lenses, enter the optical multiplexer by an inclined angle, iterate internal reflection within the optical multiplexer as being multiplexed with other optical beams, and are output as a single multiplexed beam. The inclined angle of the optical multiplexer and the thickness thereof determine the axes of the optical beams.
A Japanese Patent Application laid open No. H01-101511A has disclosed an optical system for multiplexing optical beams each output from a laser diode (hereafter dentoed as LD) and collimated by a collimating lens. The collimated beams enter a concentrating lens but at points different from others. The concentrating lens concentrates thus entered collimated beams on a point.
As a volume of information to be transmitted drastically increases, a new type of an optical transceiver widely called as Centum Form factor Pluggable (hereafter denoted as CFP) has been developed. However, there is no end to request further increase of the transmission capacity by limited power consumption. An optical transceiver with smaller sized and reduced power consumption compared with CFP is eagerly requested in the field. Such an optical transceiver generally needs an enhanced coupling efficiency between an external optical fiber and an optical signal source. The optical systems those disclosed in prior arts described above do not always satisfy the requests.